Green’s Dictionary of Slang

a phr. of greeting (cf. howzit? phr.).

1912		Bulletin (Sydney) 3 Oct. 47/1: I knew him by sight – everybody did; but had never spoken to him, and I wondered what moved him to address me. / ‘How is it?’ I inquired, affably. / ‘Dry – very dry,’ he replied.
1919		E. Dyson ‘Hello, Soldier!’ ‘Hello, Soldier!’ 86: ’Ello, Jumbo, how is it?
1947		C. Willingham End as a Man (1952) 70: ‘Jocko!’ sang out Albert Wilson [...] ‘How’s it there, boy?’.
1953		E. Hunter ‘Vicious Circle’ Jungle Kids (1967) 31: Hey, Cole. How’s it, man?